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Workshop on Modern
Evaporative Cooling
Technologies
Residential Overview
July 10, 2007
Larry Kinney
Synertech
Systems Corp
There’s a new breed of
evaporative coolers
They are no longer your basic swamp cooler;
more efficient, installed in attics or on
sidewalls, not necessarily on roof tops
Can provide many years of trouble-free
service; media lifetimes 5 to 10 times greater
than old-style excelsior
Easier on the grid than conventional A/C by a
factor of 4 or more; similar kWh savings
Greater comfort, greater control, much less
water use
Efficient media makes a big difference
High coefficient of heat
transfer
Water dripping across face
performs cooling and
cleaning function
Residue ends up in sump
Greater thickness yields
greater efficiency, with
greater pressure drop
Thus, low fan speed
optimizes efficiency
Dry and wet bulb temperatures
“Dry bulb” temperature is the temperature of air measured with a thermometer whose sensing element is dry. The weather channel talks dry bulb.
If a thermometer’s sensing element is surrounded by a wet wick over which air is blown, the sensor is evaporatively cooled to its “wet bulb” temperature.
When the relative humidity is at 100%, there is no difference between dry and wet bulb temperatures. But, as the relative humidity of the air drops, so does the wet bulb temperature with respect to dry bulb temperature.
How much cooling?
The cooling effect depends on the
temperature difference between dry and
wet bulb temperatures, the pathway and
velocity of the air, and the quality and
condition of the media.
1% Wet bulb temps in the US. 70ºF or
below works for most people
(Source: Roy Otterbein)
Direct and indirect
Delivery temps (ºF) at 99% wet bulb
(it’s hotter only 1% of the summer)
City Dry bulb
ambient
temp
Wet bulb
ambient
temp
Temp
delivered @
85%
effective-
ness
Temp
delivered @
105%
effective-
ness
Albuquerque 93 60 65 58
Denver 90 59 64 57
Las Vegas 106 66 72 64
Phoenix 108 70 76 68
Annual energy savings: 1800 ft2, HERS 89, EER 11
DX A/C vs evap cooler @ 100% effectiveness
(Energy 10 simulation, current OASys system
performance data, EER of 77)
City Conventional
DX (kWh/yr)
Evap cooler
(kWh/yr)
Savings
(kWh/yr)
Albuquerque 2,487 354 2,133
Denver 1,935 276 1,659
Las Vegas 4,722 673 4,049
Phoenix 6,043 861 5,182
Water use in electric power
generation
Thermal power plants use about 0.47 gal/kWh
generated in the US
Conservative number of the SW (coal country) is 0.5
gal/kWh
Hydro is 18 gal/kWh!
P. Torcellini, N. Long, and R. Judkoff. NREL/CP-
550-35190. November 2003. “Consumptive Water
Use for U.S. Power Production.” Available
electronically at
http://www.nrel.gov/docs/fy04osti/35190.pdf
Water consequences of
evaporative cooling (gallons/yr)
City Source
DX A/C
Source
Evap
Source
Save
Evap
@ Site
% ave
HH use
Net
Evap
Alb 1,244 177 1,067 3,699 2.7% 2,633
Den 968 138 830 2,878 1.8% 2,049
Vegas 2,361 336 2,025 7,024 2.7% 4,999
Phoen 3,022 430 2,592 8,989 5.3% 6,398
Evap cooler site water use more than made
up for by either a low-flow showerhead or a
low water use toilet Assumptions: 2.0 gpm shower head replaces 3.5 gpm shower
head; 3 six minute showers per day
1.5 gallon per flush toilet replaces 4.0 gallon per flush toilet; 10 flushes per day
-15,000
-10,000
-5,000
0
5,000
10,000
Den
ver
Alb
uque
rque
Las V
egas
Phoenix
Low F
low S
hower
Low F
low T
oilet
Ga
llo
ns
pe
r Y
ea
r a
t S
ite
Conclusions
Energy savings from the best evaporative coolers
average 86% in the Southwest; demand savings similar;
paybacks usually instantaneous versus conventional
DX.
Water use is quite modest; most of it is made up for at
the source.
This assumes an efficient home; more wasteful homes
will yield better absolute savings.
Demand of conventional A/C will lead to new power
stations.
Evaporative cooling an elegant, straightforward solution.
New Coolerado cooler
Arvada firm with indirect evap technology, new thermodynamic cycle
Adds no moisture to air stream
Model R600 delivers 1500 cfm air at 2ºF above wet bulb
May be ducted or not
Can use a portion of return air since it is dry
Performance in Boulder area
for home modeled above
5.4 tons of cooling (64,800 Btu/hr) with 1.2 kW (4100 Btu/hr) input
15.8 COP, 54 EER
Uses 12 gallons per hour of water
To deliver cooling for the season, only 330 cooling hours, 400 kWh of electricity, 3960 gallons of water (a 3.5 gpm shower uses that much in two months)
Annual cost for cooling home: $40 for electricity, $7.33 for water = $47.33
Coolerado hybrid (see
www.coolerado.com)
New model of OASys available
OASys indirect/direct has excellent
performance, elegantly-simple design
Adobe’s new through-the-wall cooler
Simple design and installation, mounts in wall
Works with new or retrofit; aesthetic appeal
Good efficiency for a direct evaporative cooler
Through-the-wall is an easy
installation
It’s best to keep evaporative
coolers in the shade.
Be sure to use with batch
water (“Clean Machine”) not
continuous bleed.
Simple connection to water
source akin to frig auto ice
maker.
Water use nicely matched to
needs of the garden.
Remote control for Slim Wall
Makes it easier to control the cooler; ideal for elderly and handicapped
Simple operation, nothing complicated
Controls all functions save for maintenance
Included with Adobe unit at no additional cost
N.B. bottom buttons: “high vent and low vent”
Thermostat
Colorado is blessed with high diurnal temperature swings; it gets chilly on most nights.
Napping a bit after dinner while leaving the cooler on can cause serious chilliness.
Simple thermostat solves problem gracefully.
Wireless install takes two minutes, must have line-of-sight to cooler.
What’s needed on the
hardware side?
We need to make annual maintenance more
efficient, lower the risk of freezing.
We need to enhance the performance of up
ducts.
We need to develop simpler, super-efficient
coolers with smarter electronic controls.
We need to explore systems that separate the
media from the fan.
Label
SunPower installs many of these coolers in weatherization
client homes, leaves this label in a conspicuous place.
Also brief the clients; this is back up.
Maintenance issue
No matter how hard we try, there will always be the risk of freezing water lines.
The bane of the evaporative cooler industry.
It would be nice to be able to push a button and cut off water at the source and drain the supply line to the cooler—then push it again and be able to operate the unit.
An advantage to all evaporative cooler users, especially elderly and handicapped.
Won’t eliminate the need for seasonal maintenance, but will keep lines from freezing and causing real problems.
Conceptual design
Mounted on the cooler side of
a saddle valve, the water
source
Tube from valve to cooler
uphill all the way
Ball valve with two positions:
top shows summer operation,
bottom winter
Operated by a small gear
motor so no power draw
except when valve actuated
Simple switch-actuating motor
Up Ducts
When evaporative coolers supply cool air to a home, they also pressurize the home.
If windows are open, cool air flows to these openings in the conditioned envelope.
However, if “up ducts,” a kind of back-draft damper, are installed in the attic floor, exhaust air flows through them into the attic and outside through existing attic vents.
This cools the home and lowers attic temperatures without the need for opening windows.
The result is better security in the home and potentially good cooling distribution.
The problem Up ducts currently available in the
market place are flimsy.
They are also without insulation and
tend to leak.
The spring mechanism puts
maximal force to open them even
without pressure differences.
Accordingly, they tend to leak all of
the time.
This is a real energy problem when
the cooler is off (like during the
heating season).
Here’s the result of an experiment made of
polyisocyanurate, with angles crudely cut
using a table saw with a plywood blade
Weights and balances
The beaded chain is very
flexible; it constrains the lid
from opening >85 degrees
from horizontal.
The weight slides on the chain
quite easily.
In the fully-down position, the
vector pulling down the lid is
maximal; when fully up, the
weight has virtually no effect
Action
The action of the weight allows for the lid to be shut except when there’s substantial pressure to open it.
It’s sealed until needed.
Yet it should be easy for the evaporative cooler’s blower to keep a number of these up ducts fully open.
Instead of transverse grills, Rob
deKieffer has designed nifty ways
of allowing air movement above
interior door ways
Evaporative coolers: separating
media from the fan
Takes advantage of
existing fans, whole
house or window.
Allows for slim through-
the-wall cooling element.
Inexpensive.
Retrofit or new.
Conceptually akin to evap
coolers used in
greenhouses
Evaporative cooler flexibility
Case shown envisions a window fan and one or more wall or window-installed evaporative media.
Simple louvered grill on inside directs cool air.
Outside insulating shutters are key to thermal performance during off cycle and provide nice aesthetics.
Europeans have known for centuries that
shutters make sense; an insulating shutter
can also save Euros in Europe and $ in the US
Installation on vintage country home.
(Imagine an evaporative cooler behind
the shutter on the left.)
Smart controls
Controls need to be developed that not only
vary fan speeds and control water cleaning
cycles, but also monitor efficiency
performance to signal the need for
maintenance.
Most important, there’s a need to think of
modern evaporative coolers as systems that
should be thoroughly integrated into energy-
efficient structures.
There’s
plenty left
to do in
policy and
marketing
On the policy side, since evaporative coolers are well matched to Colorado where population growth is high, utility and government policies that promote evaporative coolers instead of conventional cooling will delay building more generating plants and associated distribution facilities.
We must change the market! (Supplying a high-quality, low-flow shower head for free with a modern evaporative cooler could be the basis of a powerful advertisement campaign; “this simple shower head more than makes up for annual cooler water use!”) $2.07 for this model, 1.5 gpm works well!
Questions? Answers?
Feedback?
Larry Kinney
Synertech Systems Corp
1335 Deer Trail Road
Boulder, CO 80302
303-449-7941 (V)
303-579-1439 (C)
www.SynertechSystemsCorp.com